It is currently known to use a partially saponified polyvinyl alcohol emulsifier having a degree of saponification between about 60 and 90 mole percent and a solubility-in-methanol index at 55.degree. C. of at least up to about 60 percent. An example of such an emulsifier is Poval L9 sold by Kurara Co., Ltd. of Japan. This emulsifier has advantages in that it can be used at lower concentrations and it results in superior polymerization product, namely, the product has improved porosity and low gel content. However, in the past, it has not been known how to take advantage of the use of this emulsifier in "hot charge" reaction vessels. Specifically, at temperatures above 40.degree. C. the emulsifier causes an unstable suspension and difficulties in particle size control.